Source: ESPN 
Cobb suffered the injury late in the second quarter of Sunday’s win over the Baltimore Ravens. The 23-year-old Cobb likely will miss two weeks, a source told ESPN NFL Insider Adam Schefter.
Update: It’s now believed Cobb will miss eight weeks due to a fractured fibula.
Bad news for Green Bay — worse than thought RT @TyDunne : Packers WR Randall Cobb will miss 6-8 weeks with a fractured fibula.
— Adam Schefter (@AdamSchefter) October 14, 2013 
Adding to report from @TyDunne  on Cobb, sources says Randall Cobb's best-case scenario is 4 week absence and worst-case is 8 weeks.
— Chris Mortensen (@mortreport) October 14, 2013